490 THE BRAIN. 



the dura mater or other sensitive parts, produces, by reflex action, 

 muscular twitching on the same side of the body. 



The existence of these excitable points in the cerebral convolutions 

 does not show that they are nervous centres for the immediate pro- 

 duction of voluntary movement. On the contrary, we know that the 

 parts of the brain containing them, and, in some animals, even the whole 

 hemispheres, may be removed and yet the power of movement in the 

 limbs may be preserved. But they are evidently points from which an 

 influence may extend inward toward the central parts of the brain, excit- 

 ing there the immediate cause of motor action ; and this influence is 

 transmitted through the cerebral substance by definite paths, as much 

 so as that passing in the ramifications and fibres of the peripheral motor 

 nerves. 



The only doubt which has been entertained in regard to the signifi- 

 cance of these experiments is that which attributes the muscular con- 

 traction, not to the galvanization of the convolutions themselves, but to 

 a diffusion of the electric current from without inward, and a consequent 

 extension of the galvanic stimulus to the deeper parts of the brain, espe- 

 cially the corpus striatum and ascending fibres of the crus cerebri. But 

 the conditions of the experiment show that this is not the case. When 

 the distance between the two electrodes, and consequently the length of 

 the current traversing the surface of a convolution, is only one milli- 

 metre, their application to a particular spot may produce, many times 

 in succession, a definite muscular contraction ; and yet their application 

 to other spots not more than five millimetres distant from the first, and 

 equally near the base of the brain, may be entirely without effect. 



Furthermore, direct proof of the part taken by the convolutions in 

 the production of these phenomena is supplied by the experiments of 

 Braun 1 and Putnam. 2 In these experiments points were found upon 

 the cerebral convolutions which produced, under the application of elec- 

 tric stimulus, the usual definite muscular contractions. A horizontal 

 section was then made at a depth of one or two millimetres beneath the 

 surface, leaving the flap in place but cutting off the anatomical con- 

 tinuity of brain tissue. The irritation, being then reapplied to the 

 original spot, failed to excite any muscular contraction ; but if the flap 

 were turned up and the electrodes applied to the cut surface beneath, 

 a current of similar or slightly increased strength again produced the 

 same movements as before. Repeated trials of this kind, the flap being 

 alternately removed and readjusted, yielded the same results. It is 

 evident, therefore, that when the electrodes, applied to the surface of the 

 uninjured brain, cause movements on the opposite side of the body, this 

 effect is not due to a diffusion of the electric current itself toward the 

 base of the brain, but to a nervous stimulus originating in the convolu- 

 tions, and thence transmitted inward by the fibres of the white substance. 



1 Centralblatt fur die Medicinischen Wissenschaften. Berlin, June 13, 1874, 

 p. 455. 



2 Boston Medical and Surgical Journal, July 16, 1874. 



